Far from being just another number your doctors will give you, your baby's birth weight is an important figure to know.

What determines birth weight?

Birth weight is determined by multiple interacting factors. These include genetics; how many weeks your baby has been gestating; the quality and quantity of mum’s food during gestation; any disease and illness; smoking, alcohol and drug consumption; the sex of the baby; and whether the baby is part of a multiple pregnancy (twins, triplets etc.).

What is an average birth weight?

The average birth weight of babies born between 37 and 42 weeks (full-term) is 3.4kg for females and 3.5kg for males. Most babies fall somewhere between 2.5kg and 4kg.

Why is it important to know?

A low birth weight can be a sign or symptom of other health complications. It’s also important to know and track a baby’s weight because most healthy babies experience reasonably consistent weight gains over the first days, weeks and months of their lives.

Health professionals will track a baby’s weight gain against a chart of weight-for-age. These charts show the normal range and progress of weight gain and be used an indicator for whether a baby is experiencing problems putting on weight. This can be a sign of a health problems or an issue with feeding, with weight loss a particular cause for concern.

So while your baby’s starting weight might not be important by itself, it provides a useful figure for charting their health and progress over the weeks and months to come.